PROJECT SUMMARY Opioid analgesics are powerful painkillers that effectively treat pain. However, these medications carry a strong risk of dependency and may lead to death when taken at high doses. In the past two decades, opioid related mortality has nearly quadrupled and considerable efforts have been made to curb abuse. One commonly promoted tool to address the prescription opioid overdose epidemic is the establishment of Morphine Equivalent Daily Dose (MEDD) thresholds. MEDD is a measurement that converts opioid prescriptions to their equivalent dose in morphine and divides the total prescription by days supply. This measurement allows comparison among different types of opioid formulations and strengths. These thresholds are then used to limit prescribing above a given level. The values of these thresholds vary significantly by the states and organizations that set them and are used in different ways to regulate prescribing behavior. For example, a doctor may receive an automatic alert urging caution when exceeding the threshold or they may require prior authorization from a third party prior to dispensing the prescription. Organizations that use MEDD thresholds include state health departments, workers' compensation boards, Medicaid, Medicare, and the Veteran's Administration. These thresholds have been determined almost exclusively by expert opinion or adapted from other states and are generally not informed by clinical trials or observational studies. A comprehensive list of these guidelines does not exist and, to date, evaluations of MEDD threshold guidelines have been limited to Washington State. Broadly, this project seeks to characterize existing MEDD threshold policies in the United States and to evaluate the impact of a selection of these policies on prescribing behaviors and patient outcomes. Specific Aim 1 is to develop a comprehensive list of policies that includes year of implementation, threshold level, enforcement mechanism, level of evidence, and dissemination strategy. Aim 2 will focus on 4-6 policies from Aim 1 implemented each by state workers' compensation boards and state health departments on prescribing levels. Aim 3 will evaluate the impact of the same guidelines from Aim 2 on time until return to work, and opioid poisonings and adverse events. Aims 2 and 3 of this project will make use of two large, geographically diverse datasets. The first is a workers' compensation claims dataset from American International Group (AIG), a large, national workers' compensation insurer. The second is a commercial claims dataset from Truven Health MarketScan which includes data from 350 payers. Both datasets contain multiple years of data which cover pre- and post- periods for multiple guidelines of interest. Datasets include information on diagnoses, procedures, and prescriptions filled as well as basic demographic information including age, sex, and state of residence. This study has direct policy implications and may inform states or organizations who are considering adopting or revising MEDD threshold policies.